P1021: ERYTHROCYTOSIS, THROMBOCYTOSIS AND RATE OF RECURRENT THROMBOEMBOLIC EVENT - A POPULATION BASED COHORT STUDY
Authors: A. Enblom-Larsson, B. Andreasson, H. Holmberg, M. Liljeholm, A. Själander
Journal: HemaSphere (2022)

Background: The diagnosis and management of myeloproliferative neoplasms (MPN), polycythemia vera (PV) and essential thrombocythemia (ET) are well established. Other conditions with elevated hemoglobin (Hb), hematocrit (HCT) or platelets (Plt) are not as studied and there are no international accepted guidelines of how to use phlebotomy and anticoagulants to reduce thromboembolic complications. Aims: To assess the frequency of elevated blood values in patients diagnosed with a thromboembolic event, defined as myocardial infarction, ischemic stroke, transient ischemic attack, peripheral arterial thromboembolism, pulmonary embolism, deep venous thrombosis or abdominal thrombosis, and how many of these patients should be examined further to find an underlying MPN, according to the 2016 revised WHO classification. The second aim is to investigate if individuals with elevated Hb, HCT or Plt have a higher rate of first recurrent thromboembolic event depending on underlying condition. Methods: All patients over the age of 18 years with a thromboembolic event as defined above during 2017 and 2018 in the county of Norrbotten (population n=250 230) were included (n=3931). From medical records data of elevated blood values according to the 2016 revised WHO criteria of PV and ET (Hb >16.5g/dL in men, Hb >16.0g/dL in women, HCT >0.49 in men, HCT >0.48 in women or Plt >450 x109) were retrieved, as well as underlying health conditions, recurrent thromboembolic events and death. Results: In total 29.6% (1165/3931) had elevated Hb/HCT or Plt. Elevated Hb/HCT was seen in 12.7% (501/3931), 4% (159/3931) had elevated Hb/HCT at the time of initial thromboembolic event. Underlying conditions causing secondary erythrocytosis was found in 25.5% (128/501). A MPN-diagnosis was found in 1.8% (9/501), and 72.7% (364/501) had an unexplained erythrocytosis. Elevated Plt were found in 17.3% (680/3931). Of these, 91.0% (619/680) had an obvious reactive thrombocytosis while 2.4% (16/680) were diagnosed with MPN. The remaining 6.6% (45/680) had unexplained thrombocytosis. Thrombocytosis at the time of initial thromboembolic event was found in 1.3% (51/3931). In total 35% (405/1165) of the patients with elevated Hb/HCT or Plt should be investigated further to rule out MPN according to current guidelines. Of these, 41 patients had thrombocytosis, 360 erythrocytosis and 4 patients had both. A recurrent thromboembolic event was found in 11% (434/3931), of these 9.7% (42/434) had elevated Hb or HCT and 18.7% (81/434) elevated Plt. The highest rate of recurrent events per 100 years was seen in the group with unexplained elevated platelets (8.11, 95% CI 2.37-13.84). Patients with secondary erythrocytosis and unexplained thrombocytosis had the most inferior event-free survival, 2.30 years (95% CI 1.95-2.64) and 2.51 (1.98-3.04). On the other hand, patients with unexplained erythrocytosis displayed an event free survival even surpassing that of patients without erythrocytosis or thrombocytosis 3.72 (3.55-3.89) vs 3.27 (3.2-3.3) years respectively. Image:Summary/Conclusion: Elevated Hb/HCT or Plt is common in patients with arterial or venous events, affecting almost one third of all patients (1165/3931), out of these one third (405/1165) should be investigated further to rule out MPN. Secondary erythrocytosis and unexplained thrombocytosis were associated with the worst event-free survival while patients with unexplained erythrocytosis were less prone to a recurrent thromboembolic event. These results highlights the importance of finding underlying cause of elevated blood values to reduce risk of recurrent thromboembolic event.